I ran the older version of them on my Group n ish car for years on gravel and never broke one, they are designed to enable the suspension to lift up and down, that is as long as you fit them correctly, if you turn them 90degrees then they with pull the bolts out till they snap. then bolts do nothing whilst the car is going forward on that set up really other than locate the position, the load is very minimal on the bolts. going up to an M12 will not change a thing on that im afraid andy.

My WRC ones only have an M10.